The present invention relates to an ignition apparatus for an internal combustion engine, particularly relates to a winding structure of a coil.
In recent years there is proposed an ignition apparatus provided with a plurality of ignition plugs for each cylinder for firmly igniting a mixture gas having a low fuel rate to realize low fuel cost. In the case of a 4 cylinder engine, each of cylinders #1 through #4 is provided with ignition energy twice as much as that in the case of one piece of an ignition coil by feeding electricity from respective 2 pieces of ignition coils and therefore, the mixture gas can firmly be ignited and combusted.
There is an ignition system which is proposed in a prior art and disclosed in JP-A-6-33857. FIG. 10 shows an outlook view thereof. As is apparent from FIG. 10, for example, a 4 cylinder internal combustion engine is provided with 4 pieces of ignition coils 10, 20, 30, 40, and respective cylinders #1 and #4 as well as #2 and #3 utilize group ignition in which respective 2 pieces of cylinders are brought into a relationship of strokes of the internal combustion engine opposed to each other. Taking an example of the ignition coils 10 and 40, a first output terminal constituting an electrode having + polarity is connected to an ignition plug provided at #1 cylinder and a second output terminal constituting an electrode of − polarity having inverse polarity is connected to an ignition plug provided at #4 cylinder via a high voltage cord. Further, similar connections are also constituted in the ignition coil 20 and the ignition plug 30 related to #2 and #3 cylinders.
According to the above-described respective ignition coils 10 through 40, high voltages induced at secondary windings by cutting to conduct electricity to primary windings are applied to the ignition plugs from the output terminals having + polarity and − polarity, that is, both ends of the secondary windings such that polarities inverted to each other are constituted for the respective cylinders. Thereby, the high voltages generated from the first and second output terminals of the respective ignition coils are consumed as ignition energy only in the ignition plugs on sides of cylinders disposed in an explosion stroke. Whereas in an exhaust stroke which is brought into a relationship of being opposed to a compression stroke immediately before the explosion stroke, pressure in the cylinder is low and therefore, a discharge voltage of the ignition plug is about 1 kV, the pressure in the cylinder disposed in the explosion stroke immediately after the compression stroke is high, the discharge voltage becomes about several 10 kV and almost all of electric power is consumed.
FIG. 11 shows an ignition apparatus disclosed in JP-A-2001-234842 as a further advanced ignition system. As is apparent from FIG. 11, there is proposed an ignition apparatus of a structure in which a + electrode side and a − electrode side of an ignition coil provided at each of cylinders are respectively directly connected to a + polarity ignition plug and a − polarity ignition plug of the same cylinder. FIG. 12 shows a constitution view of the secondary coil of such an ignition coil. The secondary coil is constructed by a constitution of starting to wind a secondary copper wire 82, around a secondary bobbin 80 from a secondary terminal 84a to finish to wind to a secondary terminal 84b.     [Patent Reference 1]
JP-A-6-33857    [Patent Reference 2]
JP-A-2001-234842
However, according to the above-described ignition apparatus, the ignition energy is transmitted via the high voltage cord and therefore, there poses a problem of producing energy loss at the high voltage cord and taking cost in the high voltage cord per se.
According to a system of abolishing the high voltage cord and directly connecting the secondary coil of the ignition coil to the same cylinder, outputs of the both electrodes are constituted by the + polarity for carrying out + discharge and the − polarity for carrying out − discharge and therefore, in the case of supplying a voltage required for igniting the engine, when, for example, each of the both electrodes needs a voltage of 30 kV, a potential difference of 60 kV is produced between the output terminals, and insulation breakdown is brought about between the two output terminal portions caused by the potential difference to thereby cause a failure in the ignition apparatus.
Further, since the + polarity and the − polarity are generated in the output of the ignition coil, the electrode of the − potential which is easier to consume than the electrode of the positive potential by being impacted by positive ions produced by the discharge, differs in the two ignition plugs, and there poses a problem that a center electrode is selectively consumed in the first ignition plug and an outer electrode is selectively consumed in the second ignition plug.
Further, although it is generally said that in discharge of the ignition plug, − discharge is more excellent than + discharge in an energy efficiency, according to the ignition apparatus having the above-described constitution, + discharge and − discharge are utilized and an improvement therein is also desired. It is an object of the invention to provide an ignition apparatus resolving the problem, capable for preventing insulation breakdown and at the same time, capable of outputting a voltage component for only − polarity or + polarity of a high voltage output having an excellent energy efficiency and provided from a secondary coil.